The present application relates to optical interleavers, and in particular to a resonator based interleaver using a Fresnel rhomb.
It is well known to those skilled in the art of optical dense wavelength division multiplexing (DWDM) that an xe2x80x9cinterleavingxe2x80x9d effect is an efficient and cost-effective means for multiplexing or de-multiplexing optical signals. The interleaving function combines or separates two optical beams, each of which is comprised of signals at a multitude of equally spaced carrier frequencies. With reference to FIG. 1, each of the two beams, beam 1 and beam 2, is comprised of signals whose carrier frequencies are spaced xcex94xcexd, which is at twice the spacing of the combined signal. The absolute carrier frequencies of these two beams are offset from one another by one-half the frequency spacing of the carrier frequencies in those two beams. This interleaving functionality is highly desirable when constructing optical communications systems employing DWDM technology. Previously, it has been shown that an interleaving effect can be created by the coherent sum and difference of light reflected from two Gires-Tournois Interferometer (GTI) etalon resonators whose phase responses are offset from each other by xc2xd of their free spectral range (FSR). Copner et al in U.S. Pat. No. 6,125,220 issued Sep. 26, 2000, describe a polarization-insensitive interleaver, which uses a non-polarizing beam-splitter coupled with offset cavities to generate this effect.
In another known interleaver device, the required phase offset is produced by a birefringent crystal element inserted into the cavity of a single GTI etalon resonator to create two independent and properly offset optical paths within one resonator structure. U.S. Pat. No. 6,169,604 issued Jan. 2, 2000 to Cao describes an etalon-based interleaver, which derives a 180xc2x0 phase difference using an intra-cavity phase biasing element. This device has the disadvantages of complexity of construction, fragility, and high manufacturing cost.
An object of the present invention is to overcome the shortcomings of the prior art by providing a bulk resonator device that does not require complex manufacturing techniques and that does not rely on a birefringent crystal to induce a phase change.
Accordingly, the present invention relates to a resonator device comprising:
a first reflective surface on a first end face for receiving an input optical beam having S and P components, for reflecting a reflected portion of the input optical beam, and for passing a transmitted portion of the input optical beam;
a second reflective surface for receiving the transmitted portion at an angle resulting in total internal reflection of the transmitted portion, which results in a phase shift between S and P components of the transmitted portion;
a third reflective surface for receiving the transmitted portion from the second reflective surface at an angle resulting in total internal reflection of the transmitted portion, which results in a phase shift between the S and P components of the transmitted portion; and
a fourth reflective surface for receiving the transmitted portion from the third reflective surface, and for reflecting a returning portion of the transmitted portion back via the third and second reflective surfaces to the first reflective surface.
Another aspect of the present invention relates to an interferometer device comprising:
a first port for launching an input optical beam comprising first and second sets of wavelength channels;
first resonator means;
a beam splitter for separating the first set of wavelength channels from the second set of wavelength channels;
a second port for outputting the first set of wavelength channels; and
a third port for outputting the second set of wavelength channels.
The first resonator means includes:
a first reflective surface for reflecting a first portion of the input optical beam, and for transmitting a second portion of the input optical beam;
a second reflective surface for receiving the second portion of the input optical beam from the first reflective surface at an angle resulting in total internal reflection of the second portion of the input optical beam, which results in a phase shift between first and second components thereof;
a third reflective surface for receiving the second portion of the input optical beam from the second reflective surface at an angle resulting in total internal reflection of the second portion of the input optical beam, which results in a phase shift between the first and second components thereof; and
a fourth reflective surface for receiving the second portion of the input optical signal from the third reflective surface, and for reflecting substantially all of the second portion of the input optical beam back to the first reflective surface via the second and third reflective surfaces;
whereby interference between the first and second components results in the first set of wavelength channels being out of phase with the second set of wavelength channels.
Another aspect of the present invention relates to an interleaver device comprising:
an input port for launching an input optical beam comprising odd and even sets of signals;
beam splitting means for splitting the input optical beam into first and second sub-beams;
first Fresnel rhomb resonator means;
second Fresnel rhomb resonator means;
a first output port for outputting the odd set of signals; and
a second output port for outputting the even set of signals.
The first Fresnel rhomb resonator means includes:
a first reflective surface having a reflectivity R1 on a first end thereof, which is optically coupled to the beam splitting means, for receiving the first sub-beam, and for passing a first transmitted portion thereof;
a second reflective surface receiving the first transmitted portion at an angle resulting in total internal reflection thereof causing a phase shift between S and P components of the first transmitted portion;
a third reflective surface receiving the first transmitted portion from the second reflective surface at an angle resulting in total internal reflection thereof causing a phase shift between the S and P components of the first transmitted portion; and
a fourth reflective surface having a reflectivity R2 on a second end thereof for reflecting substantially all of the first transmitted portion back towards the beam splitting means.
The second Fresnel rhomb resonator means includes:
a fifth reflective surface having a reflectivity R3 on a first end thereof, which is optically coupled to the beam splitting means, for receiving the second sub-beam, and passing a second transmitted portion;
a sixth reflective surface receiving the second transmitted portion at an angle resulting in total internal reflection thereof causing a phase shift between S and P components of the second transmitted portion;
a seventh reflective surface receiving the second transmitted portion from the sixth reflective surface at an angle resulting in total internal reflection thereof causing a phase shift between the S and P components of the second transmitted portion; and
an eighth reflective surface having a reflectivity R4 on a second end thereof for reflecting substantially all of the second transmitted portion back towards the beam splitting means;
whereby the first and second sub-beams interfere causing the odd set of signals to be out of phase with the even set of signals.